Mortgage Payment Calculator

Last updated: August 4, 2026  ·  Reviewed by the DoCalc team

What Is a Mortgage Payment?

A monthly mortgage payment is rarely just one number — it's usually a bundle of four to six separate costs rolled into a single bill. Lenders call the core of it PITI: Principal (the portion that pays down what you borrowed), Interest (the lender's charge for the loan), property Taxes, and homeowners Insurance. On top of that, if your down payment is under 20%, you'll typically also pay Private Mortgage Insurance (PMI), and if your home is in a homeowners association, HOA dues stack on separately. This calculator adds all of it together so the number you see is the number that will actually leave your bank account each month.

It's worth separating these pieces mentally, because they behave very differently over time. Principal and interest are fixed for the life of a fixed-rate loan — same payment every month for 15 or 30 years. Property taxes and insurance, by contrast, can rise from year to year regardless of your mortgage rate, and PMI disappears entirely once you build enough equity. A payment that looks affordable today can shift as those variable pieces change, which is exactly why it's worth checking them individually rather than only watching the total.

The Formula

Where M is the monthly principal & interest payment, P is the loan amount (home price minus down payment), r is the monthly interest rate (annual rate ÷ 12), and n is the total number of monthly payments (loan term in years × 12). This is the standard amortization formula used by virtually every fixed-rate mortgage lender — property taxes, insurance, PMI, and HOA dues are calculated separately and added on top, since none of them affect how the loan itself amortizes.

How the Calculation Works

Amortization is front-loaded toward interest. Early in the loan, most of each payment covers interest on the large outstanding balance, and only a small slice reduces principal. As the balance shrinks over time, the interest portion of each payment shrinks with it, and more of the same fixed payment goes toward principal instead — which is why the loan pays off faster in its later years than its early ones, even though the monthly payment itself never changes on a fixed-rate loan.

This is also why extra principal payments are so effective early in a loan's life: paying down principal ahead of schedule reduces the balance that all future interest is calculated on, which compounds over the remaining term. A single extra payment in year 2 saves meaningfully more total interest than the same extra payment made in year 25, when most of the balance is already paid down.

Worked Example

A $400,000 home, 20% down ($80,000), financed at 6.75% over 30 years:

Add property tax at the 1.1% national-average rate ($400,000 × 1.1% ÷ 12 ≈ $367/mo) and $1,500/year homeowners insurance (≈ $125/mo). Because the down payment is exactly 20%, PMI doesn't apply here — total monthly payment comes to roughly $2,567. Over the full 30-year term, this loan pays about $427,000 in interest alone, more than the original loan amount, which is the trade-off a 30-year term makes for a lower monthly payment.

15-Year vs 30-Year: When to Use Each

Factor	15-year	30-year
Monthly payment	Higher	Lower
Interest rate	Typically lower	Typically higher
Total interest paid	Significantly less	Significantly more
Payment flexibility	Less room in monthly budget	More room for other goals
Best for	Higher income, prioritizing payoff speed	Maximizing monthly cash flow or investing the difference

Pros and Cons

Pros of a larger down payment: smaller loan amount and monthly payment, avoids PMI above 20%, less total interest paid, more built-in equity from day one.

Cons of a larger down payment: ties up more cash that could otherwise go toward emergency savings, investing, or other goals; a smaller down payment can still be the right call if the alternative is depleting savings entirely.

Who Should — and Shouldn't — Use This Calculator

Use it if you're comparing home prices, down payment sizes, or loan terms and want a realistic full-payment estimate — including taxes and insurance — rather than just the bare principal & interest figure many simpler calculators show.

Skip or adjust for it if you're evaluating an adjustable-rate mortgage (this models fixed-rate amortization only), or if you already have a formal Loan Estimate from a lender — that document's numbers are the ones to actually budget against, since it reflects your real credit profile and the lender's actual fees.

Common Mistakes to Avoid

The most common mistake is budgeting only against the principal & interest figure quoted in a home listing or ad, then being surprised when taxes, insurance, and PMI add hundreds of dollars more to the real monthly bill. A second mistake is assuming property tax rates are the same everywhere — they vary enormously by state and even by county, so the 1.1% national-average default here is a starting point, not a substitute for checking your specific local rate.

A third mistake is treating a mortgage pre-approval amount as a spending target rather than a ceiling — lenders often approve more than a comfortable monthly budget can absorb once real-world costs like maintenance, utilities, and HOA dues are added on top of PITI. A fourth is forgetting that PMI isn't permanent: many buyers overpay for years without realizing they can request its removal once they've built 20% equity.

Expert Recommendation

Run this calculator with your actual local property tax rate and a real homeowners insurance quote before treating any number as a budget — the national averages used as defaults here can be off by a meaningful margin in high-tax states or high-risk insurance regions. Once you have real figures, compare the resulting total monthly payment against the 28/36 rule above, not just against what a lender says you're approved to borrow.

Frequently Asked Questions

Conclusion

A mortgage payment is really five or six smaller numbers wearing one trench coat. Knowing what's inside — and which parts are fixed for decades versus which can shift year to year — turns a single intimidating monthly figure into something you can actually plan a budget around.

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